The first detection of abundant carbon in the early universe

Oct 06, 2011

Figure 1: The optical image of TN J0924-2201, a very distant radio galaxy at z = 5.19, obtained with the Hubble Space Telescope. (c) NASA/STScI/NAOJ.

(PhysOrg.com) -- A research team of astronomers, mainly from Ehime University and Kyoto University in Japan, has successfully detected a carbon emission line (CIVλ1549) in the most distant radio galaxy known so far in the early universe. Using the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope, the team observed the radio galaxy TN J0924-2201, which is 12.5 billion light years away, and was able to measure its chemical composition for the first time. Their investigation of the detected carbon line showed that a significant amount of carbon existed as early as 12.5 billion years ago, less than a billion years after the Big Bang. This important finding contributes to our understanding of the chemical evolution of the universe and may provide clues about the chemical nature of humans, who are composed of various elements such as carbon and oxygen.

Our universe began with the Big Bang, about 13.7 billion years ago. Hydrogen and helium were the only elements in this newly created universe. If these were the only elements, when and how did other elements, the so-called "metals" heavier than hydrogen and helium, originate? The answer lies in the stars shining in the night sky. Supernovae phenomena as well as nuclear fusion in stars have given rise to the variety of elements that exist today. Chemical enrichment of the universe has progressed through the birth and death of numerous stars over an immense cosmological timescale. Understanding the chemical evolution of the universe reveals a lot about the evolution of the universe itself and the sources of our human chemistry.

Astronomers have studied chemical evolution by measuring the metallicity of astronomical objects at various redshifts. Metallicity refers to the abundance of elements heavier than hydrogen and helium that occur in celestial objects. Redshifts relate to how much a wavelength has been stretched by the expansion of the universe; the greater the redshift value (z) for a galaxy, the more distant it is in time and space. Therefore, measurement of the spectra of galaxies with greater redshift values provides information about the metallicity of the early universe. Radio galaxies are particularly appropriate objects for such measurements since they shine so brightly in optical as well as radio wavelengths.

Figure 2: The deep optical spectrum of TN J0924-2201 obtained with FOCAS on the Subaru Telescope. The red arrows point to the carbon emission line (CIVλ1549).

The current research team concentrated their efforts on measuring the metallicity of a radio galaxy at a redshift higher than had been investigated in the past. Although their previous research yielded measurements of the metallicity of radio galaxies with redshift values of less than four, their findings suggested that the main epoch of major metallicity evolution had occurred at even higher redshifts, during a much earlier time. Therefore, they focused their observations on TN J0924-2201 (Figure 1), the most distant radio galaxy known; it has a high redshift value of more than 5 (z = 5.19) and is 12.5 billion light years away.

Using FOCAS on the Subaru Telescope, they obtained a deep optical spectrum of the galaxy and successfully detected, for the first time, a carbon emission line (CIVλ1549) from its ionized nebula (Figure 2). It appeared that TN J0924-2201 had already experienced significant chemical evolution at z > 5. The detection of this emission line in this early galaxy confirmed their conjecture that an abundance of metals was already present in the ancient universe as far back as 12.5 billion years ago--at z > 5. The research opens the door for future investigations of the metallicity of galaxies in the early universe with redshift values of more than five.

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So...are they able to create a baseline measurement? I mean, just to test for sure that the intergalactic medium is indeed empty enough not to affect the results...I mean, this is my biggest issue with current cosmology - that it basically relies on the assumption that seemingly empty intergalactic space is truly empty...Its not that I disagree with the results, but until they have a framework to help quantify what type of observation bias you may get, I have to take the majority of measurements at this length with a bit of a grain of salt.

Sure Tuxford. If you read the article, you might have seen "Chemical enrichment of the universe has progressed through the birth and death of numerous stars over an immense cosmological timescale." IOW, supernovae happened.

Also, AGN can contribute to the metallicity of the primordial universe (see my first link above).

Astronomers can detect many intergalactic clouds (at many different redshifts) through the study of distant astronomical sources. Indeed, these are important probes of the Inter-Galactic Medium. See, for example, the lyman-alpha forest: http://en.wikiped...a_forest

So did they test for lyman alpha forest carbon before announcing the result? From the wikipedia article, it explains that there are spectral lines for helium, carbon, silicon, etc. At that distance, it would be difficult to directly detect all interceding clouds, especially without an equally distant lightsource in the area to use as a reference measurement. It appears highly likely that there can be a margin of error, so the signal would have to be fairly strong to be conclusive.

Many of the "families" of lines associated with material between Earth and this galaxy have been identified in previous studies. According to the discovery paper this deep spectrum of TN J0924-2201 identified the line(s) for CIV with a S/N ratio of ~10!: http://arxiv.org/...16v1.pdf [Sec. 3]

I mentioned the detection of CIV *lines* because this galaxy has an AGN with a Narrow-Line Region, a region near the nucleus where the gas velocity is particularly high. At the resolution of the Subaru spectra, 0.86nm, the double-peaked nature of this feature is evident (see Fig 2 above). The double-peaked nature of the CIV line alone is pretty strong evidence for this carbon being associated with this radio galaxy and not an intervening dust cloud (not to mention the detection of other identified spectral lines with similar redshifts).

@yyz - After I wrote my comment, I intended to update it on second reading of the article (Still withing my 3 minutes to edit), but I was unable to due to issues Physorg had with the commenting system last night. I realized I was still a bit off the mark. Thanks!